Systems, methods, and compositions for production of synthetic hydrocarbon compounds

ABSTRACT

A process and system for producing hydrocarbon compounds or fuels that recycle products of hydrocarbon compound combustion—carbon dioxide or carbon monoxide, or both, and water. The energy for recycling is electricity derived from preferably not fossil based fuels, like from nuclear fuels or from renewable energy. The process comprises electrolysing water, and then using hydrogen to reduce externally supplied carbon dioxide to carbon monoxide, then using so produced carbon monoxide together with any externally supplied carbon monoxide and hydrogen in Fischer-Tropsch reactors, with upstream upgrading to desired specification fuels—for example, gasoline, jet fuel, kerosene, diesel fuel, and others. Energy released in some of these processes is used by other processes. Using adiabatic temperature changes and isothermal pressure changes for gas processing and separation, large amounts of required energy are internally recycled using electric and heat distribution lines. Phase conversion of working fluid is used in heat distribution lines for increased energy efficiency. The resulting use of electric energy is less than 1.4 times the amount of the high heating value of combustion of so produced hydrocarbon compounds when carbon dioxide is converted to carbon monoxide in the invention, and less than 0.84 when carbon monoxide is the source.

RELATED US APPLICATION DATA

This application claims the benefit of U.S. Provisional Application No.60/661,923, filed 16 Mar. 2005, and U.S. Provisional Application No.60/678,174 filed 6 May 2005, each of which are incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates generally to the field of hydrocarbon compoundproduction and, more specifically, to energy efficient processes andsystems that produce hydrocarbon compound fuels. In a preferredembodiment, the invention relates to an apparatus and a method toconvert electric energy into hydrocarbon compound fuels, such asgasoline, kerosene, jet fuel and diesel fuel, among others, and whichare produced by recycling products of combustion—carbon dioxide andwater.

BACKGROUND OF THE INVENTION

Although the idea for developing synthetic hydrocarbon fuels has beendiscussed for at least the last 30 years, there has not been a need toproduce them because of the availability, ease of production,transportation, and processing of fossil fuels. However, the worldwidefossil fuel market is changing due to a number of factors, includingsteadily increasing worldwide energy demand, increasing concentration ofproduction in oil producing regions, and increasing emphasis in oildependant countries on the importance of energy supply.

There are several disadvantages to using fossil fuels. First, there is afinite amount of fossil fuels available which, once used, cannot beregenerated. Additionally, hydrocarbon fuels made from fossil fuels maycontain highly undesirable sulfur, nitrogen, and aromatic compounds.When these fuels are burned, sulfur, nitrogen, and particulates arereleased into the air, which leads to the formation of acid rain andsmog. More recently, concern has focused on the impact of carbon dioxideemissions from fossil fuel combustion as a contributor to globalwarming.

There are several well-established processes for direct hydrogenation ofgases such as carbon monoxide or carbon dioxide to produce hydrocarbonfuels. One of the most successful was developed in Germany in the 1920sby Franz Fischer and Hans Tropsch.

In 1938, early German plants produced approximately 5 million barrelsper year of diesel oil and gasoline using the Fischer-Tropsch process,which reacts carbon monoxide and hydrogen over a catalyst to produceliquid hydrocarbons and water. The problem with this and other methodsis that they use fossil fuels such as coal or natural gas to produce thecarbon monoxide. The use of such fossil fuels as the primary feedstockis accompanied by many of the same drawbacks as the production of fossilfuels such as finite supply and emissions.

Therefore, it can be seen that there is a long-felt need for aproduction system that recycles the products of combustion intohydrocarbon compound fuels. It is to such a system and processes formaking hydrocarbon compounds that the present invention is primarilydirected, with emphasis on energy efficiency.

SUMMARY OF THE INVENTION

The present invention comprises systems, methods and compositions forthe production of synthetic hydrocarbon compounds, particularlyhydrocarbon compounds that can be used as fuels. In general, species ofcarbon oxides, carbon monoxide or carbon dioxide, are converted into oneor more hydrocarbon compounds, comprising carbon and hydrogen, includingbut not limited to diesel fuel, gasoline, jet fuels, liquefied petroleumgas, or compounds found in natural gas. A particular process comprisesforming, with electricity, a hydrogen stream, and in the presence of atleast a portion of the hydrogen from the hydrogen stream, converting atleast a portion of the carbon monoxide present in a carbon monoxidestream, into a hydrocarbon compound.

In a preferred embodiment of the system with a carbon dioxide input, theamount of input electric energy needed to convert carbon dioxide intohigh heating value of output hydrocarbon compounds combustion energy isin a range of between 1.4 and 1.1. In another preferred embodiment ofthe system with a carbon monoxide input (thus eliminating the need toconvert carbon dioxide to carbon monoxide), the external electric energyneeded to convert carbon monoxide is between 0.64 and 0.84 of the highheating value of hydrocarbon compounds. That is, in an embodiment of thepresent invention using carbon dioxide as an input, more electric energywill be required than the high heating value of combustion ofhydrocarbon compounds produced. In another embodiment of the presentinvention, using carbon monoxide as an input, less electric energy willbe required than the high heating value of combustion of hydrocarboncompounds produced.

According to an aspect of the present invention, it is possible toproduce within one plant on the order of five hundred thousand gallonsof fuel per day, or even more, in case sufficient electric energy,carbon monoxide and/or carbon dioxide are available.

One aspect of the invention comprises systems and methods comprising anelectrolyser and a Fisher-Tropsch reactor, and in some embodiments, alsoa reverse water gas shift reactor, for producing hydrocarbon compounds.The present invention comprises methods and systems for producinghydrocarbon compounds comprising converting at least a portion of one ofthe species of carbon oxide, including but not limited to carbonmonoxide, into hydrocarbon compounds, via a Fischer-Tropsch process inthe presence of at least a portion of the hydrogen stream; andtransferring at least a portion of excess heat from the Fischer-Tropschprocess to one of the other process steps in the method or system, to aportion of a method or system requiring energy, or one of the otherunits in the system, for example, to an electrolyser or a reverse watergas shift reactor.

In the present invention, there are numerous places where certain gasesmust be separated from a gas mixture, or for example, gas parameterssuch as temperature and pressure, must be changed to make one or bothcompatible with an upstream or downstream process. These separations orchanges to gases in the invention consume large amounts of energy. It isa novel aspect of the invention that energy can be transferred withinthe invention to meet the energy needs for gas separations and changes.

One advantage of the present invention is its energy efficient gasprocessing. There are generally two energy efficient thermodynamicprocesses used for gas processing. The first one is an adiabatic processwhen all external work is converted to or from gas energy. The secondone is an isothermal process, when all external work is either convertedinto heat or derived from heat. By recycling external work through anelectrical distribution line and heat through several heat distributionlines, energy losses in gas processing are substantially reduced. Thisis also assisted by use of phase conversion of working fluids in heatdistribution lines to accept or deliver heat energy.

The present invention comprises systems and methods that provide theability to produce a variety of hydrocarbon compounds, such as compoundsfor different fuels and a degree of control in producing one or morespecific types of hydrocarbon fuels that is not found with currentlyavailable methods for making synthetic fuels. These and other objects,features and advantages of the present invention will become moreapparent upon reading the following specification in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 illustrate general, high-level systems of the presentinvention, according to preferred embodiments.

FIGS. 5-6 illustrate preferred embodiments of the present invention,incorporating the systems of FIGS. 1-4.

FIG. 7 shows various configurations of energy distribution lines of thepresent invention.

FIG. 8 shows a principal of operation of an RWGS reactor subassemblyaccording to a preferred embodiment of the present invention.

FIG. 9 illustrates a three-stage RWGS reactor with carbon dioxiderecycling, according to a preferred embodiment of the present invention.

FIG. 10 shows an RWGS reactor with a heater, according to a preferredembodiment of the present invention.

FIG. 11 shows a principal of operation of an FT reactor subassemblyaccording to a preferred embodiment of the present invention.

FIG. 12 shows a two stage FT reactor, according to a preferredembodiment of the present invention.

FIG. 13 illustrates an FT reactor with a water cooler, according to apreferred embodiment of the present invention.

FIG. 14 shows a portion of the hydrogen unit of the present invention,electrolyser cells, according to a preferred embodiment.

FIG. 15 illustrates one example of electric power feed to anelectrolyser of the present invention, according to a preferredembodiment.

FIG. 16 illustrates various winding arrangements of phase shiftingtransformers.

FIG. 17 is a graph of electrolyser voltage according to a preferredembodiment of the present invention.

FIG. 18 shows a fuel post processor system according to a preferredembodiment of the present invention.

FIG. 19 illustrates a burning system according to a preferred embodimentof the present invention.

FIG. 20 illustrates a flow chart of an energy efficientelectro-mechanical gas separation process.

FIG. 21 shows adiabatic machines according to a preferred embodiment ofthe present invention.

FIG. 22 shows isothermal gas mixture pressure changers according to apreferred embodiment of the present invention.

FIG. 23 illustrates a combination condenser and evaporator according toa preferred embodiment of the present invention.

FIG. 24 illustrates electrical energy distribution and recycling linesaccording to a preferred embodiment of the present invention.

FIGS. 25-26 illustrate heat distribution and recycling lines accordingto a preferred embodiment of the present invention.

FIG. 27 shows a cooling loop for FT reactors according to a preferredembodiment of the present invention.

FIG. 28 shows steam/water feed to the electrolyser according to apreferred embodiment of the present invention.

FIG. 29 shows the RWGS subassembly main loop control according to apreferred embodiment of the present invention.

FIG. 30 shows the FT subassembly main loop control according to apreferred embodiment of the present invention.

FIG. 31 shows the RWGS subassembly hydrogen supply control according toa preferred embodiment of the present invention.

FIG. 32 shows the FT subassembly hydrogen supply control according to apreferred embodiment of the present invention.

DETAILED DESCRIPTION

The present invention comprises systems, methods and compositions formaking hydrocarbon compounds. Complete combustion of hydrocarbon fuelslike coal, natural gas, liquid petroleum gas, ethanol, methanol,gasoline, kerosene, diesel fuel, and other known fuels primarily resultsin two basic substances—carbon dioxide and water. When burning suchfuels, the main reaction is as follows:

C_(n)H_(2n+2)+(n+(2n+2)/2)*O₂→Combustion energy (High HeatingValue)+n*CO₂+(2n+2)/2*H₂O (water).  (1)

For example, for an average value of n=10, 10% more moles of water isproduced than carbon dioxide. The number of oxygen moles used is equalto a sum of one mole for oxidizing carbon and a half of a mole plus 10%to oxidize hydrogen, 1.55 moles in total. As used herein, “High HeatingValue” (HHV) is the amount of heat produced by the complete combustionof a unit quantity of fuel when all products of the combustion arecooled down to the temperature before the combustion and the water vaporformed during combustion is condensed.

In the invention described herein, the products of combustion, carbonoxides and hydrogen are recombined into hydrocarbon compounds, such astransportation fuels, including but not limited to, diesel and gasoline.It is also possible to recombine them into other compounds andcompositions such as natural gas or liquefied petroleum gas. As usedherein, hydrocarbon compounds include hydrocarbon compounds that may beused as an energy source such as fuels.

Hydrocarbon compounds may be produced using a Fischer-Tropsch process.In this part of this process and system, carbon monoxide (CO) andhydrogen are ideally reacted as follows:

CO+2H₂→(—CH₂—)+H₂O  (2)

wherein (—CH₂—) is a building block for polymerization into longercarbon chains. The primary products of this polymerization are linearparaffins, C_(n)H_(2n), plus two hydrogen atoms to complete any chain atthe ends. In this reaction, one hydrogen molecule is used for formationof hydrocarbons, plus approximately 10% for completing chains at theends, and another hydrogen molecule is used to reduce carbon monoxide tocarbon.

There are a variety of processes to produce carbon monoxide from carbondioxide. One method for this is a chemical process called reversewater-gas shift reaction (RWGS). This reaction is as follows:

CO₂+H₂

CO+H₂O  (3)

In this reaction a hydrogen molecule is needed to reduce carbon dioxideto carbon monoxide.

For the reactions shown here, a ratio of 1.1+1+1=3.1 hydrogen moles perone carbon dioxide mole is used to produce hydrocarbon compounds. Ifwater is to serve as the source of the hydrogen, the calculation may beas follows:

Externally supplied water 1.1*H₂O+

Water from RWGS reaction H₂O+

Water from Fischer-Tropsch reaction H₂O+

Electric energy for water electrolysis=3.1*H₂+3.1/2*O₂  (4)

In an ideal situation, the amount of oxygen released is the same amountas was consumed in combustion thereby completing the recycling process.In the methods and systems taught herein, all or a portion of the waterused can be from outside sources as well. A variety of processes may beused to produce hydrogen from water, for example, electrolysis of watermay be used to produce hydrogen, photosynthesis may be used to producehydrogen, as well as the heating of water to produce hydrogen. Waterelectrolysis is selected in the preferred embodiment while other methodsof producing hydrogen are known to those skilled in the art and may becontemplated by the present invention.

One aspect of the invention comprises systems and methods comprisingpreferably an electrolyser, a reverse water gas shift reactor, and aFisher-Tropsch reactor for producing hydrocarbon compounds. The presentinvention comprises methods and systems for producing hydrocarboncompounds comprising converting at least a portion of one of the speciesof carbon oxide, including but not limited to carbon monoxide, into oneor more hydrocarbon compounds, via a Fischer-Tropsch process in thepresence of at least a portion of a hydrogen stream; and transferring atleast a portion of excess thermal energy from the Fischer-Tropschprocess to one of the other process steps in the method requiringenergy, or one of the other units in the system, for example, to anelectrolyser or a reverse water gas shift reactor.

An electrolyser may be used to separate water into a hydrogen gas streamand a stream of oxygen gas.

The process may further comprise the conversion of a species of carbonoxide, including carbon dioxide. This step of converting one or morespecies of carbon oxide may comprise converting carbon dioxide in areverse water gas shift (RWGS) process. The conversion of CO₂ takesplace in the presence of hydrogen, and hydrogen may be provided by atleast a portion of the hydrogen from the hydrogen stream from theelectrolyser. Conversion of carbon dioxide to carbon monoxide may beaccomplished by any methods known to those skilled in the art and suchmethods are contemplated by the present invention.

The carbon monoxide stream for the present invention may be providedfrom any source, for example, a source may be a stream of carbonmonoxide from a source separate from and outside the present invention.A second source of carbon monoxide is as a portion of the effluentstream from the optional reaction process converting carbon dioxide to,among other species, carbon monoxide. The carbon dioxide stream for thisprocess may come from a source such as carbon dioxide waste from asource outside the present invention.

The effluent from the Fischer-Tropsch process may undergo an upgradingprocess, upgrading the spectrum of hydrocarbons into the hydrocarboncompositions desired, such as various liquid fuels. As used herein,“upgrading”, “post-processing” and “refining” or “upgrade”“post-process”, and “refine” are used interchangeably and mean toseparate, isolate, purify or in some manner differentiate by chemical orphysical characteristics the various hydrocarbon compounds present fromthe synthesis reaction in the Fischer-Tropsch reactor, for example,fractionize, and convert the compounds into usable products or feedstockfor other processes. Examples of conversion processes include, but arenot limited to, oligomerisation, hydrocracking, isomerisation,aromatization, hydrogenation, hydroisomerisation, and alkylation.

As used herein, “C₃ compound” means a compound having three carbonatoms. For example, propane would be a C₃ hydrocarbon compound.

As used herein, “C₄ compound” means a compound having four carbon atoms.For example, butane would be a C₄ hydrocarbon compound.

As used herein, “C₅₊ compound” means compounds having five or morecarbon atoms. For example, hexane, octane, and compounds such as benzenewould be a C₅₊ hydrocarbon compound.

In an embodiment of the present invention, systems and methods toproduce hydrocarbon compounds from the products of fuel combustion(carbon oxides) are described, and comprise providing an amount ofelectricity, such as electricity from a nuclear reactor, to a plantusing a portion of the amount of the electricity to form a hydrogenstream from water; and reacting at least a portion of the products offuel combustion, carbon dioxide and carbon monoxide, in the presence ofat least a portion of the hydrogen from the hydrogen stream to formhydrocarbon compounds; wherein use of electric energy is minimized byrecycling energies consumed and released in various processes.

In a preferred embodiment, the methods and systems of the presentinvention convert the input electric energy into the high heating valueof output hydrocarbon compounds combustion energy in a range of between1.4 and 1.1, when carbon dioxide is used as a carbon oxide in themethods and systems, and between 0.64 and 0.84 when carbon monoxide isthe carbon oxide in the methods and systems, or without conversion ofcarbon dioxide to carbon monoxide.

In an embodiment of the present invention, electricity is used for theconversion of carbon dioxide and/or carbon monoxide and water intohydrocarbon compounds comprising carbon and hydrogen, wherein a waterelectrolyser is used to supply hydrogen to the conversion process. Thecarbon dioxide may be externally supplied to the process, and convertedto carbon monoxide for further use in the methods and systems of thepresent invention. The carbon monoxide may also be externally suppliedto the process, and a mixture of carbon oxides can be supplied as well.

The systems, methods and plants of the present invention may incorporatea number of subsystems, each aiding in the overall efficiency andproductivity of the entire process, system or plant. For example, theinvention may incorporate a source of electric energy, an electrolyser,a RWGS reactor, an FT reactor, and a post-processing plant.

In an embodiment of the present invention, there is a source of electricenergy generated from the heat of a nuclear reactor. An example is afast breeder reactor. This reactor may be setup once with reprocessednuclear waste, and then its nuclear core may be reprocessed at areprocessing plant. This has the advantage of extending the energyoutput from the world's uranium reserves on the order of 25 fold or so.At typical re-processing intervals of five years, there is plenty ofinitial fuel to power the present invention until the end of thephysical plants' useful life. Alternatively, the energy may be providedby nuclear reactor waste heat conversion, a thermochemical process, orother sources, including fossil fuel free electricity, such as hydro,solar, ocean waves, wind, tides or currents, and combinations of any ofthese sources.

Electric energy may be used to electrolyse water to create hydrogen andoxygen. In some embodiments, the electrolyser may need a substantialamount of heat for operation. This heat, together with water for theoperation, may be supplied by steam generated elsewhere in the plant.

While hydrogen may be produced by conventional electrolysis of waterusing electrodes, other methods can be employed, including thethermolysis of water (for example using waste heat from nuclearreactors), thermochemical processes, and combinations of these methods.Oxygen produced in the electrolyser may be put to uses outside of theplant.

The process of electrolysing water for the production of hydrogenpreferably includes an electrolyser comprising bipolar electrodes and acell average operating temperature over 100° C., or over 130° C.,wherein cell internal pressures are over 10 bar, or over 20 bar. Otherembodiments include that the electric current density is over 3,000A/m², that a stack of cells is used with voltages over 60 V, and/or thatAC-to-DC voltage rectifiers are used, with an output voltage ripple lessthan 3%.

There are numerous uses in the plant for the hydrogen produced in theelectrolyser. Among them, hydrogen and carbon dioxide can be usedtogether in the RWGS reactor to produce syngas, a mixture of carbonmonoxide and hydrogen.

A source of carbon dioxide for the present process is a plant emittingcarbon oxides, such carbon dioxide or carbon monoxide as a byproduct,especially a plant that is required to reduce its carbon oxideemissions. Examples of such a plant include a blast furnace used toproduce steel, and fossil fuel power plants using coal or gas to produceelectricity. Carbon dioxide, carbon monoxide or carbon oxides or amixture may be provided by any method, including but not limited to,externally provided from any source.

A method of converting carbon dioxide to carbon monoxide is through theuse of a RWGS reactor. An aspect of the invention comprises methods andsystems wherein carbon dioxide and hydrogen are supplied to a RWGSreactor, and there is a substantially complete conversion of carbondioxide to carbon monoxide, for example, a conversion of over 70%, morepreferably over 80%, and more preferably still, over 90%. The output oreffluent stream of the RWGS reactor comprises carbon monoxide andhydrogen in a H₂/CO ratio of between zero and three. Further, there areincluded means of separation of a portion of carbon dioxide on theoutput, and recycling of the carbon dioxide to the input. Otherpreferred embodiments may include that the operating temperature isbetween 350-500° C., that there is provided steam separation bycondensation, and that more than one reactor can be sequential, seriallyconnected. An embodiment may comprise intermediate separation of steambetween serially connected RWGS reactors.

As a byproduct of the RWGS reactor operation, water is produced that maybe used to feed an electrolyser.

A syngas effluent, which is generally a mixture of carbon monoxide andhydrogen and some residual carbon dioxide, is fed from a RWGS reactor toan FT reactor. Additional hydrogen may be added to the syngas, or tocarbon monoxide, as required for the desired output of an FT reactor. Itis also possible to use carbon monoxide, such as waste carbon monoxidefrom existing industrial processes, and combine this carbon monoxidewith hydrogen instead of, or in addition to, the syngas stream producedby the RWGS reactor. Aspects of a plant of the present invention includemethods that use carbon monoxide without the need for the intermediatestep of converting carbon dioxide to carbon monoxide, thereby bypassingthe RWGS process.

An FT unit of the present invention, which may include more than one FTreactors, primarily provides conversion of carbon monoxide and hydrogento hydrocarbon compounds, at rates that are desirable, for example, aconversion of over 70%, more preferably over 80%, and more preferablystill, over 90%. In the present invention, the methods and systemsprovide that the reaction heat removal is at substantially isothermalconditions. Additionally, the hydrogen supply is controlled, forexample, for minimum production of methane and ethane. Other embodimentsinclude that steam and gaseous hydrocarbon output separation usingcondensation caused by change of both temperature and pressure areprovided, and that more than one FT reactor may be sequential orserially connected or having more than one reactor operating atsubstantially different temperatures and associated operatingconditions.

The catalyst for the FT reaction can be a metal such as iron, cobalt,nickel, and combinations thereof; a metal oxide such as iron oxide,cobalt oxide, nickel oxide, ruthenium oxide, and combinations thereof;support-type material such as alumina or zeolites; supported metals,mixed metals, metal oxides, mixed metal oxides; and combinations ofthese catalysts, and others known to those skilled in the art.

The main output of the FT reactor is a mixture of hydrocarbon compoundswith a byproduct of water that can have a variety of uses such as beingfed to the electrolyser. The FT reaction is highly exothermic, and theheat can be used in a variety of ways. For example, at least a portionof the heat can be removed by a water stream being converted to steamwith that steam then being fed to the electrolyser if required.

The mixture of hydrocarbon compounds exiting an FT reactor may be fed toa post-processing plant that can be similar, or in many ways simpler,than existing hydrocarbon fuel refineries as no removal of sulfur ornitrogen compounds is required. Some amount of hydrogen compounds can beused in this post-processing, refining process to yield compositionscomprising combustible compounds. Such compositions may be used asfuels.

Upon post-processing, desired transportation grade fuel compositions areprovided, that can include high-octane gasoline and diesel fuel of acomposition reducing or even eliminating need for after-treatment invehicles. The fuel compositions produced from the present process avoidmany of the inherent drawbacks of processing crude oil, i.e. thesecompositions have no sulfur content, no nitrogen content, and noaromatics content. They do, however, have high volumetric andgravimetric energy densities, an excellent resistance to thermaloxidation processes, are fire safe (i.e., they are hard to ignite), andgood low temperature properties.

The present system further provides for methods using separators, forseparation of gases in a gas mixture, for example, in a novel andinventive combination of heat exchangers and compressors/expanders. Thesystems may include the use of compressors or expanders with heating orcooling to condition gas mixtures for condensation of a selected gas ina mixture, wherein expanders and compressors are used to condition gasmixtures to the desired temperatures. The systems may use heatexchangers for condensation or evaporation of a selected gas, with phaseconversion of a cooling fluid into its vapor or steam as appropriate.Other embodiments include methods comprising phase conversion of aworking fluid that is used for heating or cooling, along with eithercompression or expansion of gases. Heat machines, for example, heatpumps using a compressor, can be used to move heat from a lowtemperature area to a high temperature area, and heat removers using anexpander-generator (electric power generation) may be utilized.

The present invention provides energy efficient systems that use energy,such as electric energy, for the conversion of carbon oxides, includingcarbon dioxide and carbon monoxide, and water into hydrocarbon fuels ona production scale. A system of the present invention also comprises useof residual internal heat for electricity generation, which electricityis used for carbon dioxide, carbon monoxide and water conversion intohydrocarbon fuels. A system may also comprise compressors and expandersused for conditioning and for separation of gas mixture components.

The present invention further incorporates one or more subsystemscomprising transferring heat or steam between components of the system,including the transfer of heat from FT reactor(s) to an electrolysereither directly or via conversion to electric energy, feeding reactionsteam from FT reactor(s) for condensation in an electrolyser,transferring heat from FT reactor(s) for use throughout the system byusers of heat, via the use of heat exchange methods, transferring heatfrom FT reactor(s) to RWGS reactors along with associated input/outputgas processing, heating reaction water from RWGS and/or FT reactors foruse in an electrolyser, and supplying heat to gas-liquid phaseconversion for cooling and heating of process gases and liquids.

The present invention also comprises use of gas expanders with electricgenerators and gas compressors with electric motors for receiving andfeeding electric energy, i.e. recycling, to reduce substantially overallenergy use in the plant.

The present invention as shown in FIG. 1 comprises, in essence, a methodof the present invention 100 being a method of converting one or morespecies of carbon oxides into hydrocarbon fuels F using electricity asthe energy input E. The output fuels F can include, for example,gasoline, diesel and jet fuel. FIGS. 1-4 illustrate general, high-levelsystems of the present invention 100, each embodying its own novelty andinventive step, as described below, and together, forming a preferredprocess of the present invention 100 as shown in FIGS. 5 and 6.

While it is known to produce hydrocarbon fuels from coal and gas, theuse of electricity to drive the conversion has previously been avoided.The industry has refrained from developing methods of producing fuelsfrom carbon oxides using electricity because the energy efficiencieswere simply too low to justify the cost. Yet, the energy efficiency ofthe present invention is greater than 60%; that is, the ratio of thehigh heating value of the fuels F to the amount of electricity Erequired to drive the conversion(s), is greater than 60%, and morepreferably greater than 80%. In reverse ratio, it means that the amountof electric energy is approximately lower than 1.7 ( 1/60%) times of thehigh heating value of the fuel F, and more preferably lower than 1.25times.

In yet another high level view of the present invention 100, as shown inFIG. 2, the present process comprises an energy input step 200 providingenergy to the process, a conversion step 300 converting the one or morespecies of carbon oxides to fuel F, and a hydrogen input step 400providing hydrogen to efficiently drive the conversion 300 of the carbonoxides to fuel F.

Referring to the conversion step 300 converting the carbon oxide to fuelF, as shown in FIG. 3, it can include at least two subsystems, one, acarbon monoxide conversion step 320 for the conversion of carbonmonoxide to fuel F, and a second, a carbon dioxide conversion step 360,should the process of the present invention 100 be presented with carbondioxide. The conversion step 360 converts carbon dioxide to carbonmonoxide, and then feeds the carbon monoxide to the carbon monoxideconversion step 320. Alternatively, or in combination with the carbonmonoxide from the conversion step 360, carbon monoxide can be fed toconversion step 320 from outside the system of the present invention100, for example, from a plant's carbon monoxide waste stream or amixture of CO₂ and CO can be fed to step 360 to convert CO₂ to CO.

Both conversion steps 320, 360 utilize at least a portion of thehydrogen from hydrogen input step 400 to drive their respectiveconversions. In one preferred embodiment, the invention 100 is presentedwith both carbon dioxide, and carbon monoxide, and thus the process ofthe present invention 100 utilizes both conversion steps 320, 360.

In FIG. 4, an intermediate step 500 is shown located between the outputof the conversion step 300 converting the carbon oxide, and the finalproduct fuels F. Typically, the output of the conversion step 300 is aspectrum of hydrocarbon compounds HC, out of which only some can be usedin fuels. Thus, a post-processing step 500 is provided to upgrade themto the desired compositions, for example, fuels F.

Preferred embodiments of various subsystems of the present invention 100are shown in FIGS. 5 and 6, and comprise a recycling process, and plant,to produce hydrocarbon fuels from the products of hydrocarbon fuelcombustion. The invention includes the energy input step 200 providingenergy to the process, including generating electricity using nuclearpower reactors 210, preferably using fast breeder reactors consumingexisting nuclear waste. A reactor 210 can be setup once with reprocessednuclear waste, and then its nuclear core can be reprocessed at, forexample, a re-processing plant 220 to extend the energy output from theworld's Uranium reserves, perhaps 25 fold or more. As will be understoodby those of skill in the art, at typical reprocessing intervals of fiveyears, there is enough initial fuel to power the present invention untilthe end of its useful life.

The electricity is provided to the hydrogen input step 400, which caninclude electrolysing water in an electrolyser 410 to form streams ofhydrogen and oxygen. Heat, also called thermal energy, from othersubsystems of the process of the present invention 100 can be suppliedto this step, to improve efficiencies. It can be supplied eitherdirectly to heat water when required or through conversion toelectricity to conduct electrolysis. Some known types of electrolysers410 may need some heat for operation. This heat, together with water forelectrolyser operation, is preferably supplied primarily by steamgenerated elsewhere in the system of the present invention 100. Thereare numerous uses for hydrogen produced in the electrolyser 410throughout the system, while it is preferred that most, if not all, ofthe oxygen produced is put to revenue generating uses outside the systemof the present invention 100.

At least a portion of the hydrogen is fed to the conversion step 300,which, if the system of the present invention 100 handles both carbonmonoxide and carbon dioxide, is a two-step process. In the firstprocess, a carbon dioxide conversion step 360 is employed, including areverse water gas shift process, namely a reverse water gas shift (RWGS)reactor 362, to combine hydrogen and carbon dioxide to produce syngas, amixture of carbon monoxide and hydrogen. As a byproduct of the RWGSreactor operation, steam is produced that is fed to the electrolyser410.

A source of carbon dioxide for the conversion step 360 may be a plantemitting carbon dioxide as a byproduct, especially a plant that isrequired to reduce carbon dioxide emissions. The prime examples of suchplants are blast furnaces used to produce steel, and fossil fuel powerplants using coal or gas to produce electricity.

Carbon dioxide can come in a mixture with carbon monoxide. This mixturecan be either separated into carbon dioxide and carbon monoxide orprocessed as a mixture in the reactor 362 completing conversion ofcarbon dioxide to carbon monoxide.

The syngas is then fed to the carbon monoxide conversion step 320,including a Fisher-Tropsch process to combine carbon monoxide andhydrogen to provide a spectrum of hydrocarbons based on a double bondradical. The carbon monoxide conversion step 320 can include aFischer-Tropsch (FT) reactor 322. While the FT reactor 322 can use thesyngas from step 360, it is also possible to use waste carbon monoxidefrom existing industrial processes, and combine this waste carbonmonoxide with hydrogen, instead of, or in addition to, syngas producedby the RWGS reactor 362. As is known, there are number of processes thatproduce carbon monoxide as waste, especially in combination with carbondioxide.

In one preferred embodiment of the present system of the presentinvention 100, only carbon monoxide is processed, (not carbon dioxide),as this materially eliminates the need for the RWGS process 360. Thesystem of the present invention 100 can also use a mixture of carbondioxide and carbon monoxide as waste from industrial processes supplyingsuch a mixture. Additional hydrogen can be added to the syngas output ofstep 360, and/or to the carbon monoxide input to step 320, as requiredto adjust the desired output of the FT reactor 322.

The main output of the FT reactor 322 is a mixture of hydrocarboncompounds based on —(CH₂)-radical and a byproduct is water, which ispreferably fed to the electrolyser 410. The FT reaction is highlyexothermic, so heat is removed at least by providing water, which isconverted to steam, which can be used directly or indirectly as a sourceof energy for electrolyser 410.

The hydrocarbon compounds output from the FT reactor can becharacterized as a version of crude oil, in that the hydrocarboncompounds, like crude oil, can be refined using known techniques, toyield fuel compounds. Thus, the hydrocarbons are upgraded, or refined,at step 500, including a fuel post-processing step, to produce thedesired compositions of fuels F. Step 500 can include a post-processing(upgrading) plant 510 that is similar, but generally simpler, with fewerprocessing steps needed, than in existing crude oil refineries. Suchrefining techniques are known to those skilled in the art. Again, someamount of hydrogen from step 400 may be used in this refining process500.

The present invention uses multiple energy distribution lines, gas flowrecycling/feedback loops, and inter-process heat and electricityexchanges. The overall results of the various improvements in each ofthe subsystems of the present invention 100, and in system-wideefficiencies, provide a system wherein preferably at least 60% of theenergy input to the process (for example, from the electricity generatedby the nuclear power plant) is ultimately contained in the high heatingvalue of combustion output fuels F.

The system of the present invention 100 produces beneficial byproducts,as its outputs are fuels, and oxygen. In addition, the system of thepresent invention 100 provides a critical externality in that it reducescarbon dioxide. Carbon dioxide is a greenhouse gas that, because it is aprime contributor to global warming, is the subject to a variety ofworldwide Treaties, such as the Kyoto Protocol, and national andregional implementing regulations.

As described, the final outputs of this recycling process of the presentinvention 100 are many desired transportation fuels, which can includehigh-octane sulfur free gasoline and sulfur free diesel fuel of acomposition reducing or even eliminating the need for after-treatment invehicles. One advantage of this system of the present invention 100 isits ability to produce a variety of hydrocarbon compound fuels. Anotheradvantage is the degree of control available to plant operators to alterthe ratio of hydrocarbon compounds produced by adjusting particularparameters of the methods and system, for example, the ratio of carbonmonoxide and hydrogen fed to particular FT reactors. By varying theamounts of syngas fed to different types of FT reactors, it is possibleto achieve different output ratios of diesel fuel, gasoline, jet fuel,and other fuels out of the total amount of syngas input.

The system of the present invention 100 is described in further detailbelow, including preferred embodiments of the various subsystems of theinvention.

Energy Distribution Lines

The system of the present invention 100 incorporates several energydistribution lines with two distinctive types of energy lines—electricand heat. Examples of energy distribution lines employed by the presentsystem are shown in FIG. 7. At least one electric energy distributionline (EDL) is used. For example, one EDL is a conventional three-phasealternating current electric power distribution line operating at aconventional phase-to-phase voltage in the 10-50 kV range, a rangepracticed in commonly-used electric power generators. However, othervoltages can be used as dictated by specific needs as would be commonlyunderstood by a person of ordinary skill in the art.

Numerous generators and motors are connected to the EDL in this system.Generators are preferably of a synchronous type, conventionallycontrolled to match frequency, phase, and voltage amplitudes, so theycan all feed the EDL in parallel. This type of control is used inexisting electric power grid control. Motors are preferred to be of asynchronous type for controllability, and to realize higher efficiency,but other types of motors can be used.

In a preferred system of the present invention 100, there are otherenergy distribution lines, distributing heat, or thermal energy, (asopposed to electric energy) throughout the plant. The heat distributionlines (HDL) in this system can accept heat from a heat sources, anddeliver heat to a heat users.

Phase conversion of a working fluid is used in the heat distributionlines. Each line uses two reservoirs—one of a liquid and another of avapor of this liquid, both close to the boiling temperature and pressureof that working fluid. When heat delivery is required, vapor is takenfrom one half of the line, condensed, and delivered to the liquid halfof the line. Condensation heat is released to a user of heat. When thereis a need to take heat, then liquid is taken, vaporized, and deliveredas vapor to the vapor half of the line. External heat is consumed byevaporation of working fluid.

In a preferred embodiment, there are five distinct temperatures for eachof the five heat distribution lines.

A first HDL is preferably at the operating temperature of RWGS reactor362, preferably in the range of 280-800° C. In a preferred embodiment,the operating temperature of the RWGS reactor 362 is approximately 400°C. At this temperature, it is preferred to use ethylene glycol as theworking fluid or another fluid with a similar heat of vaporization andsimilar boiling pressure at 400° C. This first HDL is used at least toheat incoming gases into a RWGS reactor, and to deliver heat to thisreactor itself, as the RWGS reaction is endothermic. In furtherdescription herein, this first HDL will sometimes be referred as the“RWGS-line”, denoting its vapor part with a “V”, and its liquid partwith an “L”.

A second HDL is preferably at the operating temperature of the FTreactor 322, preferably in the range of 180-350° C. It is preferred thatthe working fluid of this second HDL is water, as used in coal-fired andnuclear power plants. It is also possible to use a separate cooling loopfor the FT reactor operating at higher temperatures using other workingfluids, for example, ethylene glycol, and exchange some or all of itsheat into this second HDL. In further description herein, this secondHDL will sometimes be referred as the “FT-line”, denoting its steam partwith an “S”, and its water part with a “W”.

A third HDL is at a temperature of water in the electrolyser 410. Forexample, it can be in 100-150° C. range, preferably in 130-140° C.range. The main purpose of this third HDL is to feed the electrolyser410 with water and/or steam. This third HDL preferably uses water as aworking fluid. In further description herein, this third HDL willsometimes be referred to as the “E-line”, denoting its steam part withan “S”, and its water part with a “W”.

A fourth HDL is at ambient temperature, at 25° C. in an example of apreferred embodiment of the system, but can be at other ambienttemperatures at various locations and weather conditions of this system.The working fluid can be a common refrigerant used at such ambienttemperatures. The primary use of this fourth HDL is for the processingof incoming and outgoing materials. In further description herein, thisfourth HDL will sometimes be referred to as the “A-line”, denoting itsvapor part with a “V”, and its liquid part with an “L”.

A fifth HDL is preferably at the operating temperature of carbon dioxideseparator 372 on FIG. 8, preferably in the range of −50 to −55° C. Atthis temperature, it is preferred to use common refrigerants likeethylene. This fifth HDL is used for heating and cooling gases flowingto and from the carbon dioxide separator. In further description herein,this line will sometimes be referred to as the “C-line”, denoting itsvapor part with a “V”, and its liquid part with an “L”.

An additional source of available thermal energy is nuclear power plantwaste heat that can be used by converting it to electric energy.

Energy Distribution Lines Balancing

The energy distribution lines should be balanced, so the incoming energyshould be equal to outgoing energy. The electrical distribution linedelivers electric energy for water electrolysis and numerous motorsdriving compressors and feed pumps. It receives electric energy fromnumerous gas expanders driving electric power generators, includingexpanders converting heat energy released in the FT reactors or throughburning of residual gases. The balance of electric energy is deliveredby an external source 210.

The RWGS-line is balanced in a preferred manner by a heat pumpdelivering energy from the FT reactors. Throughout the system of thepresent invention 100, there are uses of heat energy from this line byconverting its vapor to liquid.

In a preferred embodiment, the FT-line is balanced by heat coming fromcooling FT reactors.

In a preferred embodiment, the E-line is balanced by heat coming fromcooling FT reactors.

In a preferred embodiment, the A-line is balanced by delivering energyto the environment. This line collects excess thermal energy notconsumed by the process, or converted to electricity. The primary usecan be in space heating, especially in cold weather, by convertingA-line vapor into liquid. If there is no need in this heat, then it canbe dissipated to the environment using, for example, a conventional heatexchanger.

For economic construction, there should be a typical temperaturedifference between the temperature of the environment—air or water—andthe temperature of this line. Operating (boiling) temperature in thisline can be varied by regulating pressure.

In a preferred embodiment, the C-line is balanced by a heat pumpremoving excess heat and delivering it to the A-line.

Energy Input

Energy input step 200 preferably comprises an electric power plant 210using heat generated by a nuclear process. While many types of nuclearprocesses can be used, if a fast breeder type reactor is not employed,then the plant would need a periodic supply of nuclear fuel.

The system of the present invention 100 need not use original or wasteheat of a fission reactor, as other sources of energy to generateelectricity can be used. For example, the efficiency of the system ofthe present invention 100 and the output requirements can be met notonly by nuclear energy, but also, for example, hydroelectric or windgenerators, as there is no waste heat required from an external sourceof energy. While not optimal, fossil fuel electric power plants can beused.

Carbon Oxides Conversion

Carbon Dioxide Conversion

Carbon dioxide conversion is preferably run through a RWGS process 360.As shown in FIG. 8, a preferable carbon dioxide conversion systemcomprises an RWGS reactor 362 that converts incoming carbon dioxide intocarbon monoxide using hydrogen as a reducing agent.

The basic reaction is as follows:

CO₂+H₂

CO+H₂O  (5)

This is a reversible reaction, and its equilibrium coefficient toconvert carbon dioxide to carbon monoxide is low. For this reason, inthe preferred embodiment of the present invention, excess of incominggases, both carbon dioxide and hydrogen, are used to increase the amountof carbon monoxide.

The amount of hydrogen is enough for both (i) conversion to water insidethe reactor and (ii) up to a desired level of mixture H₂/CO (syngas) tofeed the FT reactor 322. In this embodiment, this ratio H₂/CO is aroundtwo, so the amount of hydrogen moles is approximately up to three timesthe number of input carbon dioxide moles. Depending on the FT catalystused, other H₂/CO values for feed to the FT reactor are also acceptable.

The amount of carbon dioxide at the input of the reactor 362 ispreferably enough to achieve complete conversion of incoming carbondioxide at a selected operating temperature of the reactor 362. Forexample, in one embodiment, the RWGS process 360 has a 400° C. operatingtemperature, and a three-stage RWGS reactor with intermediate separationof steam. In such a design, approximately the same amount of carbondioxide is required at the input of the reactor, than incoming carbondioxide normally available, conditioned that the H₂/CO ratio on theoutput is near a value of 2. This additional amount of carbon dioxide isthus provided by a recycling loop of this reactor assembly as shown inFIG. 8. This additional supply of carbon dioxide is not consumed in thereactor, but circulates through it to change the equilibrium conditionsfor as near a complete conversion of the incoming carbon dioxide aspossible. The two streams of carbon dioxide (fresh as well as recycled)can be mixed in a conventional gas mixer 366 or fed using separate,appropriately designed nozzles or distributors into the RWGS reactor.

The amount of carbon dioxide in the recycle loop depends on the amountof hydrogen feed, on the operating temperature of the RWGS reaction, andon the number of serially connected reactors with separation of steambetween them. At lower hydrogen feed, or at lower temperatures, or withfewer reactors in series, there is a substantially larger amount ofcarbon dioxide in the recycle loop, and vice versa. One advantage ofhaving a lesser amount of gas in the recycle loop is that there arelesser electric and heat losses needed to maintain gas circulation andseparation.

The output stream of the RWGS reactor 362 goes first through a steamcondensation section 368, and then through a carbon dioxide separator372. In one embodiment, the steam condensation section can include acondenser (heat exchanger) followed by a knockout drum. The condensedwater from the separator 368 can be fed back to the electrolyser.Separated carbon dioxide is delivered to the input gas mixer 366. Adirect output of the carbon dioxide separator 372 is syngas with a H₂/COratio approximately as beneficially required by the FT reactor 322 forefficient conversion and, residual carbon dioxide, if any.

There are other well-known processes to convert carbon dioxide intocarbon monoxide that can be used in the present invention withoutchanging functionality of this apparatus.

Operating pressure in the reactors can be in the range of 4-30 bar,20-25 bar is preferred. GHSV-STP (Gas Hourly Space Velocity at StandardTemperature and Pressure) of 1,500-15,000, preferably 5,000-8,000.

Steam is preferably separated at or near ambient temperature, whichleads to high separation ratio.

Separation of carbon dioxide from the output can be accomplished bytraditional and current methods. The currently prevalent methods includea variety of Amine absorption processes as well as carbonate processes,pressure swing absorption, adsorption, and gas permeation, among others.Additionally, cryogenic separation is possible by lowering thetemperature, and increasing pressure under appropriate processingconditions, such that only 15-35% of carbon dioxide may be left in thesyngas, as a ratio to carbon monoxide, mol/mol, for example, at −50 to−55° C. and 50-100 bar pressure.

More likely, using cryogenics, solvent-mediated processes such asRyan-Holmes, or three-phase ones such as CFZ (Controlled Freezing Zone),can be used for further reduction of carbon dioxide content. Theresidual carbon dioxide will be circulated through the upstreamprocesses, or better yet beneficially consumed under certain operatingconditions in the FT subassembly, and then more or less of it will bereturned back to the input of this subassembly. Further, some of theseprocesses can be used sequentially, for example, cryogenic liquefactionto separate the majority of carbon dioxide, followed by either CFZ orAmine absorption to condition syngas to a desired carbon dioxide level,in 3-10% level measured in mol/mol versus carbon monoxide. In front ofthe cryogenic-type of separator, water vapors must be thoroughlyremoved. Adsorption type dryers may be used as commonly practiced incryogenic processes.

Another preferable carbon dioxide conversion system is shown in FIG. 9,and comprises a three-stage RWGS. As shown, there are three steamseparator sections, one after each reactor, and then a carbon dioxideseparator at the end of the process.

The RWGS reaction is weak in the direction of formation of carbonmonoxide and therefore requires removal of at least one reactant.

In order to achieve as close to 100% conversion as possible, the systemof the present invention 100 can use a three-stage RWGS reactor inconjunction with (i) steam removal on the output of each stage and (ii)increased molar concentration on the input.

First, the hydrogen molar concentration is increased to the extent thatthe resulting syngas will have up to the right ratio H₂/CO for theupstream Fischer-Tropsch reactor 322. In one example, this ratio is twoor more.

To satisfy the RWGS reaction, the first RWGS reactor 382 in thisembodiment is fed with a molar ratio of 3:1 in relation to input carbondioxide 384 molar content. One mole is used to reduce carbon dioxide tocarbon monoxide, and two moles are left for effluent syngas.

Next, the carbon dioxide input is increased to the first RWGS reactor382 by creating a recycling line 386 from the output, and circulating itwithout conversion. Approximately one more mole needs to be added in thecirculating loop to one mole of input carbon dioxide to create theapproximately 100% conversion in three RWGS reactors 382, 388, 394 inseries with the construction as presented in FIG. 9.

The carbon dioxide conversion system of FIG. 9 relies on steam removaland carbon dioxide separation. A first steam separator 392 removes steamfrom effluent gas of the first RWGS reactor 382, and by doing so,creates conditions to continue carbon dioxide conversion in the secondRWGS reactor 388. As carbon monoxide has not been removed, theconversion rate of the second reactor 388 will be smaller than the firstreactor 382.

A second steam separator 392 removes steam from effluent gas of thesecond RWGS reactor 388, and by doing so, creates conditions to continuecarbon dioxide conversion in the third RWGS reactor 394. As carbonmonoxide has not been removed, the conversion rate of the third reactor394 will be smaller than the second reactor 388.

A third steam separator 392 is positioned on the output of the thirdRWGS reactor 394. On the output of this separator, effluent gas containssyngas of a desired CO/H₂ ratio and carbon dioxide. Thus, carbon dioxideis separated using a separator 396, and placed in recycling line 386 tocombine in a gas mixer 398 with incoming carbon dioxide 384.

If syngas contains smaller amount of hydrogen than necessary to feedupstream to the FT reactors, then additional hydrogen from electrolyser410 will be added.

RWGS Reactors

The RWGS reactors used in the present system of the present invention100 can operate efficiently at a number of operating temperatures, while400° C. is used in a preferred embodiment. An exemplary catalyst isKATALCO 71-5 produced by Johnson Matthey. Operating pressures can be inthe range of 4-30 bar, with preference for higher values to reduceoverall size of the assembly. A GHSV-STP of 1,500-15,000, preferably5,000-8,000 is used.

The reaction is endothermic and requires external heat. In a preferredembodiment, the system of the present invention 100 uses an isothermaloperation (being within plus or minus 10% of the ideal operatingtemperature as measured in ° K), with external heat delivered into areaction zone from an external source. One example of an overall heatdelivery system 810 is illustrated in FIG. 10. Phase conversion of aworking fluid is used to deliver heat at or near isothermally,specifically the RWGS-line. RWGS-line vapors are delivered to condensercoil 812. Vapors condense and release condensation heat, whilemaintaining phase conversion temperature. The residual working fluid isreleased into the liquid part of the RWGS-line. Released heat isconsumed by reacting gases inside the reactor through a heat exchangeprocess.

Preferably, the reactors 382, 388, 394 of FIG. 9 are of the same generalconstruction, although the second and third reactors can be smaller thanthe first, as they convert lesser amounts of carbon dioxide into carbonmonoxide and process smaller in volume gas mixture.

This RWGS subassembly can process not only pure carbon dioxide but alsoa mixture of carbon dioxide and carbon monoxide. The mixture can beprocessed through one, two, or all three serially connected reactors, asa function of ratio of carbon monoxide to carbon dioxide. If this ratiois smaller than this ratio on the output of the first reactor undercondition of pure carbon dioxide conversion, then all three reactorswill be used. The difference will be in reduced amount of hydrogenrequired for reduced amount of carbon dioxide. The same rule willdetermine if two or only one reactors are required for processing ofthis mixture. Ultimately, if only carbon monoxide is supplied, then noreactors are required.

Alternatives—Carbon Dioxide Conversion

As discussed, carbon dioxide conversion is preferably run through anRWGS process 360. There are a number of modifications to this RWGSprocess that will not significantly change the outcome—the production ofcarbon monoxide components of syngas.

For example, the temperature of reaction in the reactors can be reduced.This will decrease the equilibrium constant, and will thus cause anincrease in amount of carbon dioxide in the recycling line, or thenumber of reactors connected in series, or both.

Additionally, the temperature of reaction can be increased, and then itcan be possible to reduce the number of reactors in a preferredembodiment from three, to two or only one with a sufficient amount ofcarbon dioxide circulation to provide 100% conversion of incoming carbondioxide.

It is also possible to reduce amount of hydrogen gas fed to this processwith consequent increase in carbon dioxide in the recycling loop. It isalso possible to reduce the amount of circulating carbon dioxide byusing more than three reactors in series at the same temperature.

The reaction heat does not have to be delivered isothermally, but rathercan be provided through heat exchange with any hot-side fluid ofappropriate temperature, flow rate, among other parameters.

Other processes are known to convert carbon dioxide into carbonmonoxide, and such processes can be used in the present system of thepresent invention 100.

Carbon Monoxide Conversion

Carbon monoxide conversion is preferably run through an FT reactorprocess 320. The reactor assembly is shown in FIG. 11. The operation ofan FT reactor 322 is as follows:

CO+2H₂→(—CH₂—)+H₂O  (6)

Dashes at (—CH₂—) denote available bonds for either adding hydrogen orfor polymerization. There are numerous straight and oxygenatedhydrocarbon compounds produced in Fischer-Tropsch reactors as a functionof the type of catalyst used, and the operating temperature, pressure,and gas velocity in the reactor.

In one preferred embodiment, as an example, the reactor operates with aCobalt catalyst at 220° C., and produces a mix of hydrocarbons, whichafter upgrading leads primarily to the production of a mixture ofgasoline and diesel fuel in an approximate proportion of 1:2.

In other implementations of the present invention, at highertemperatures, for example around 330-350° C., more gasoline is produced,in gasoline to diesel ratio of approximately 4:1. So by combiningoperation at different temperatures, one can adjust gasoline to dieselratio from 1:2 to 4:1. The production rate of diesel fuel by the presentinvention includes adjusting the temperature, pressure and residencetime (gas flow). The amount of residual hydrocarbons that is difficultto convert into desired liquid fuels varies, and generally is higher athigher temperature and lower at low temperature.

In one embodiment, a Cobalt catalyst is used, with a H₂/CO ratio of2.15, a 220° C. operating temperature, a pressure of approximately 20bar, and GHSV-STP of 1,500. The conversion of carbon monoxide tohydrocarbons is up to 75%. Pressure can change in the range of 10-30 barand GHSV from 500 to 5,000.

The FT reactor 322 on FIG. 11 produces both liquid hydrocarbons that aredrained for further processing, and gaseous hydrocarbons mixed withsteam and input gases (carbon monoxide and hydrogen). The presence ofinput gases is due to incomplete conversion of syngas. For more completeconversion, more than one FT reactor can be used in series with removalof steam and certain hydrocarbon gases in between the reactors. In anexample of a preferred embodiment, a two-stage FT reactor is used toachieve higher conversion efficiency.

On the output of the reactor 322, steam is separated from the effluentgas by a steam separator 324, then gaseous hydrocarbons with carbonnumbers C₅-C₆ by a separator 326, and finally gaseous hydrocarbons withcarbon numbers C₃-C₄ by a separator 328. These separation processes canbe combined as a function of composition of gas mixtures beforeseparation. The residual gas contains mainly natural gas compounds,methane CH₄ and ethane C₂H₆, and residual syngas gases carbon monoxideand hydrogen, and various amounts of not separated carbon dioxide and C₃and C₄ compounds.

In a preferred embodiment, a majority of the syngas is returned to theinput of the FT reactor 322 via a recycle line, thereby improvingconversion efficiency of incoming syngas into hydrocarbon fuels. Thiscan be accomplished in part by using a controllable throttle or valve332. This throttle is installed in the recycling line for effluent gas,and allows venting or flaring of a portion of this effluent gas in equalmolar proportions. In a preferred embodiment, a controlling parameter isthe amount of natural gas compounds before the vent. The throttle isopen just enough to maintain this amount at a predetermined level. Othergases can be used for the same purpose.

A gas conditioner 334 in the recycling line can be provided to match thetemperature and pressure of the syngas coming from the RWGS assembly360. Syngas is combined in a gas mixer 336, or similar to a gas mixer384.

Instead of syngas, the FT reactor 322 can be fed by an external sourceof waste carbon monoxide (from outside the system of the presentinvention 100) and hydrogen from the electrolyser 410, or a mixture ofthese gases and syngas. Hydrogen is added on the input from theelectrolyser 410 to regulate the H₂/CO ratio required by the FT reactor322. In a preferred embodiment, this H₂/CO ratio is around two, and morespecifically between 2 and 2.2.

Vented gases in this apparatus can be fed into a burner-generator toproduce electric power.

This FT assembly can be replaced by a variety of conventionalFischer-Tropsch reactor designs without changing functionality of thisapparatus. A more detailed preferred carbon monoxide conversion systemis shown in FIG. 12. A two-stage FT reactor system 340 is illustrated.There are two FT reactors 342, 344 in this assembly. Syngas from theRWGS subassembly and some amount of hydrogen from the electrolyser arefed into the first FT reactor 342. A certain amount of liquidhydrocarbons is produced and drained from the reactor. The unconvertedsyngas, steam, residual carbon dioxide from the RWGS assembly, and allhydrocarbons produced in the reactor 342 that are gaseous at thereaction temperature and pressure are fed into a steam separator 346. Itis preferred to make separation at ambient temperature, but othertemperatures can be used as well. It is possible that some hydrocarbongases will be separated along with water. The residual water andhydrocarbons then may be separated as commonly practiced, for example bydistillation or gravimetrically.

The residual syngas with some amount of hydrocarbon gases and residualcarbon dioxide are fed into a second FT reactor 344. A certain amount ofliquid hydrocarbons is produced and drained from the reactor. Theunconverted syngas, steam, residual carbon dioxide from the RWGSassembly, and all hydrocarbons produced in the reactor that are gaseousat the reaction temperature and pressure are fed into a steam separator348. It is preferred to make separation at ambient temperature, butother temperatures can be used as well.

At this position in the process, much smaller amounts of syngas are leftthan on the output of FT reactor 342, and therefore the partial pressureof hydrocarbon gases with carbon number C₅, and higher is larger, andthey will condense along with steam in the steam and C₅₊ separator 348.C_(n) is a hydrocarbon with n-number of carbon atoms per molecule.C_(n+) means hydrocarbons with n or more carbon atoms per molecule. Thecondensed liquid is drained, and water is separated by many commonprocesses, like distillation or gravimetrically in a water separator352.

The residual gases from the separator 348 are fed to another separator354 of hydrocarbons, including ones with carbon numbers C₃ and C₄. Theycan be condensed and separated from this residual mixture at, forexample, 20-50 bar, and at temperatures where most of such compounds arecondensed. This temperature depends on amount of other gases in aneffluent gas. When these amounts are large in comparison with volume ofseparateable gases, low temperature like one used for carbon dioxideseparation can be used. Then, not only C₃ and C_(n) hydrocarbons can beseparated but also carbon dioxide. These gases can be easily separatedfrom each other by pressure change and carbon dioxide recycled to theinput of the RWGS assembly. Effluent syngas, components of natural gas,and residual carbon dioxide are fed to a controllable relief 332 (FIG.11). In this relief, in equilibrium conditions, the amount of syngas issubstantially smaller than other gases, and therefore whatever amount ofmixture is released, it will contain much smaller amount of syngas thanin the recycling loop. Presence of syngas in the recycling loop has thesame effect on completion of conversion of the incoming syngas aspresence of carbon dioxide in the recycling loop of the RWGSsubassembly. Amount of syngas in vented gases can be used also forcontrol of venting ratio.

In other preferred embodiments, more reactors can be used to increasethe syngas conversion rate, even at different operating parameters, tocreate a more desirable spectrum of produced hydrocarbons, like one atlow temperature like 220° C. and another one at like 340° C. Syngas canbe directed in different amounts to reactors operating under differentconditions to regulate composition of produced hydrocarbons that will inits turn affect composition of fuels after upgrading, i.e. relativeamounts of gasoline, jet fuel, diesel fuel, and the like.

FT Reactors

The reaction is highly exothermic and requires substantial heat removalas the output of the reactor is highly temperature dependent. In apreferred embodiment, phase conversion of water into steam in theFT-line is used to remove this heat, as illustrated in FIG. 13. Thisleads to near isothermal operation of the reactor, and thereforeconsistent output, as the output of products from this reactor is highlydependent on temperature, for example within 10° C.

Alternatives—Carbon Monoxide Conversion

Carbon monoxide conversion may be accomplished through an FT process320. There are number of modifications to this FT process that will notchange the outcome, i.e. the production of hydrocarbon compounds out ofsyngas, but may significantly change the composition of the productsproduced.

For example, the temperature of the reactors can vary in the range of150° C. to 350° C. Variances in catalyst type, catalyst bed type,pressure, residence time, and velocity of syngas, will alter in varyingdegrees the composition of the products produced. At highertemperatures, lighter hydrocarbon compositions are produced. In oneexample, at 310°-340° C., and utilizing a circulating catalyst, 72% ofthe output includes compositions with carbon number C₅-C₁₁ on whichgasoline is based, 6% heavier hydrocarbons, 8% hydrocarbon gases, and14% of alcohols, ketones and acids.

The FT assembly can be made to operate at different reactor temperaturesby regulating water temperature and pressure in the FT-line, andpressure in the FT reactors and other components affect separation ofsteam and hydrocarbon gases.

The type of catalyst and its bed can be also changed from time to timeto match changes in operating characteristics. Two or more reactors canbe used connected in series and operating at the same or differenttemperatures, catalysts, and other operating conditions. Also, there canbe two or more parallel strings of reactors, also operating at differentor same conditions.

With such a construction, a plant built with system of the presentinvention 100 can accommodate changing market needs over many years ofoperation.

Generation of Hydrogen

The present system of the present invention 100 further comprises ahydrogen input step 400 providing hydrogen to drive the conversion 300of the carbon oxides to fuel F. An electrolyser is the preferred deviceto provide the hydrogen.

A portion of an embodiment of electrolyser 410 is shown in FIG. 14. Itis preferred to use bipolar electrodes 412 for a high voltage and lowercurrent stack of electrolytic cells. Electric current 414 flows throughthe surface of all bipolar electrodes into electrolyte 416, which causeselectrolysis of water in each cell.

Each cell can be divided by a gas diaphragm 418. Hydrogen and oxygen arereleased on opposite sides of each bipolar electrode, collected in thespace between electrode and diaphragm, and vented out for uses in thesystem of the present invention 100.

In a preferred embodiment, an electrolyser design with a high currentdensity, for example 5-20 kA/m², is used. In comparison with low currentdensities, for example, 1-3 kA/m², such an increase leads to muchsmaller size, weight, and cost electrolysers. But there is a differentenergy efficiency at such an increased current density due to muchlarger overvoltage on electrodes and resistive losses in theelectrolyte. High current density electrolysers use the followingconstruction and operating parameters:

-   -   Operating temperature is 130° C., and potentially up to 150° C.,        which decreases overvoltage potential on electrodes and        decreases resistivity of the electrolyte;    -   Operating pressure is in the range of 20-30 bar to decrease        volume of evolving gases that is beneficial to electrolyte        conductivity, and to decrease water vaporization and its        recycling;    -   Concentration of KOH in the electrolyte is approximately 30% by        weight; and    -   The gap between electrodes can be made smaller by use of        diaphragm materials for temperatures in 130-150° C. range.

It is possible to achieve cell voltage around its thermoneutral(isothermal) voltage at some level of high current. It means that ifwith a supply of electric energy, this thermoneutral potential isreached, then no additional cooling or heating of cells will berequired. If this potential will be lower, then additional heat will berequired, and if higher—then cooling will be required.

Reaction water to the cells of high current density electrolysers can bedelivered in two ways, either traditionally as liquid, or by steamcondensing into water right in the cell, or a combination of water andsteam. The choice is design specific, as a function of current density,other auxiliary subsystem choice for the electrolyser, operatingvoltages, among others.

Choice of high current density electrolysers leads to other efficienciesin the overall plant due to lower temperature and especially pressuredifferentials.

The electrical feed of the electrolyser can use existing devicesdescribed herein. In a preferred embodiment, FIG. 15 illustrates the useof several rectifiers connected in series, each fed from phase shiftingtransformers. This circuit design leads to a high efficiency rectifierthat converts AC (alternating current) voltage in the first EDL to DC(direct current)-required for operation of electrolysers.

The high voltage stack of the electrolyser can be divided into severalstacks working in parallel for convenience of construction, maintenance,and safety. The same can be done with the rectifier. Semiconductorrectifiers can be paralleled to carry higher current, or each of suchparallel rectifiers can be connected to a separate electrolyser stack.The same can be done with the transformers.

Referring to FIGS. 15 and 16, three transformers are used, but thesetransformers do not have to have any phase shift, and can be used inmany quantities. The high voltage electrolyser cell stacks can even befed directly without any transformer if output voltage of the electricpower plant is compatible with the stack required voltage.

The phase shifting transformers use more than one phase on the inputwith phase shifts between phases not 0° or 180°, but usually 120° or240°, as common in three-phase electrical distribution. In an example,transformer 432 with three input phases is fed by the electric powerdistribution line (EDL). The phase relationship is shown on the vectordiagram 434. This is a typical delta phase arrangement.

The output (secondary) winding of one phase of the three-phasetransformer 432 comprises typically two separate windings connected inseries. One winding 436 is wound over one input phase winding, and theother 438 is wound over another input phase winding. Phase of voltage ineach secondary winding is in phase with the input voltage of the windingover which this secondary winding is wound.

By selecting the ratio of number of turns, or transformer ratio, betweenthese two windings and polarity, one can achieve many desired phaseshifts. The diagram 442 shows a ratio in voltage transformation and apolarity of voltages transformed from its underlying input phasevoltages of equal value and 120° phase shift. The combined voltage inoutput phase XY is phase shifted in comparison with the input voltage inphase XY. In this example, it is lagging. The diagram 444 shows changeof polarity on the output which makes this phase shift leading.

Rectifier

The present system can utilize a semiconductor rectifier, being atypical three-phase rectifier. Instead of semiconductors, vacuumtube-based rectifiers that can rectify much larger current can also beused. Semiconductors can be paralleled using known circuits to achievereasonable sharing of current in paralleled semiconductors. Therectifier can also be made for more phases by adding more phase legs andconnecting all phases from all phase shifting transformers in parallel.

Output Voltage

The phase shifting transformers and rectifiers described herein arecombined into a circuit shown in FIG. 15. In a preferred embodiment,three rectifier circuits R are shown connected in series, each fed fromphase shifting transformers T. This circuit leads to a rectified DCvoltage with very slight pulsation of voltage, 1.5% peak-to-peak, whichis beneficial for sizing of all components in the electrical circuits ofthe electrolyser. There are other ways to make connection, for example,through paralleling these three circuits. Another alternative is to usea different number of circuits, with more or less phases andcorresponding lower or higher pulsation of output voltage.

The resulting voltage is a sum of voltages from all three rectifiers.FIG. 17 illustrates, to scale, a voltage diagram 452 from onethree-phase rectifier. For one period of the electric distribution linevoltage)(360°, there are six rectified tops of sine waveform, frompositive and negative halves of each phase. The depth of voltagepulsation is cos (30°=0.866, or 13.4% of the peak voltage value. In thecircuit with three rectifiers, the phase shift is maintained betweenphases to be 20° leading and lagging. In this case, the depth of voltagepulsations is cos (10°)=0.985, or 1.5% of the peak value—the voltagediagram 454.

This pulsation is adequate for low current fluctuation in theelectrolyser cells that, in turn, leads to higher utilization of thesurfaces of the cells and lower power rating of transformers andrectifiers.

The high voltage stack of the electrolyser can be divided into severalstacks working in parallel for convenience of construction, maintenanceand safety, among other issues. The same can be done with a rectifier.Semiconductor rectifiers can be paralleled to carry higher current, oreach of such parallel rectifiers can be connected to a separateelectrolyser stack. The same can be done with the transformers.

Post-Processing

Typically, the output of the conversion step 300 is a spectrum ofhydrocarbons. A post-processing step 500 is provided to upgrade thehydrocarbons to the desired mixture of fuels F. The process can useexisting technologies to convert hydrocarbon streams from the FTsubassembly into desired fuels, and other products if so desired. FIG.18 shows inputs in and outputs from such a facility. Typical upgraderswill involve hydrocracking of FT heavy ends (in the lubes and wax range)to fuels primarily in the diesel and gasoline range. It should be notedthat a refinery's need in hydrogen can be preferably satisfied withhydrogen from the electrolyser.

Burner-Generator

In a preferred embodiment, a burning system 520 is shown in FIG. 19. Theinputs to the burner can be vented gases from the FT reactor assembly,and/or residues from the refinery, and/or natural gas compounds. Allthese compounds are burned in the gas turbine-generator 522 with arelatively small portion of oxygen coming from the electrolyser. Theoutput gases from the turbine exhaust are steam and carbon dioxide.Steam is separated into water and residue carbon dioxide—that is fedback to a gas mixer with incoming carbon dioxide. This is yet anothergas recycling loop of the system of the present invention 100.

Electric power produced by the generator is fed back to the electricpower line and further to the electrolyser.

As a result, there is little to no waste material coming out of thesystem, only the desired fuels and oxygen in the amount to combust them.

As electric power produced is recycled back into production of hydrogen,this apparatus is less sensitive to incomplete conversion of syngas inthe FT subassembly. Also, as carbon dioxide is recycled back to theinput of the RWGS subassembly, this apparatus is less sensitive toseparation efficiency of carbon dioxide separation in the RWGSsubassembly.

Gas Separation and Processing Generally

In the presented processes, there are numerous places where certaingases must be separated from a gas mixture, or simply gas parameters,for example, temperature and pressure, must be adjusted to make itcompatible with an upstream process.

One advantage of the present system is its energy efficient gasprocessing. There are basically two energy efficient thermodynamicprocesses used for gas processing. The first one is an adiabatic processwhen all external work is converted to or from gas energy. The secondone is an isothermal process, when all external work is either convertedinto heat or derived from heat.

It will be understood by those of ordinary skill in the art that theseare ideal processes. In practical applications, there are sometemperature variations in an ideally isothermal process. Thesevariations make the process near isothermal. As used herein, the term“isothermal” shall include an operation or process that is “near”,“approximate” or other such terms to modify the ideal isothermaloperation, and more specifically relates to a change in absolutetemperature measured in ° K in a practical isothermal process in a rangeof plus and minus 10% from an ideal isothermal temperature. Similarly,in practical adiabatic processes, some heat energy is involved inaddition to the mainly external work performed. Such “practical”adiabatic processes are similarly “near” and/or “approximately”adiabatic, and when involved heat energy is also in a range of plus andminus 10% of the amount of external work energy from the ideal process.

The present invention preferably includes one or more units for changingthe pressure of a gas “isothermally”, which incorporates a range of plusand minus 10% from the ideal isothermal process temperature. The presentinvention preferably includes one or more units for changing thetemperature of a gas “adiabatically”, which incorporates a range of plusand minus 10% from the ideal adiabatic process, as described above.

As shown in FIG. 20, a diagram of a universal gas separation using thesetwo processes is presented. First, three processes 610 through 614condition a gas mixture for separation of one or more of its componentsby condensation in the condenser 616. Then, three processes 618 through622 condition the residual gas mixture for further processing. Theseparated gas or gases is in liquid phase in the condenser 616. If it isdesired for further processing in a gaseous phase, then some gases areevaporated in the evaporator 624, and then are conditioned for furtherprocessing by processes 626 through 630.

Each group of processes, either 610 through 614, or 618 through 620, or626 through 630, are identical in their principal functioning. They arecentered on conditioning of gases for adiabatic processing to avoid anygas mixture component from changing phase, either to liquid or solid.Each process begins with adjusting pressure isothermally. Next, the gasor mixture of gasses is processed adiabatically to change temperature.After this process, the final isothermal process changes pressure asrequired for further processing. In summary, pressure is changedisothermally, and temperature adiabatically.

FIG. 21 shows adiabatic machines, one to increase temperature andpressure by compression using power from an electric distribution line,and one to decrease temperature and pressure and generating power tothat line. In a preferred embodiment, an electric power line is used asboth a source and the recipient of power delivered to or derived fromadiabatic processes. The compressor 632 is preferred to be a turbinedriven by an electric motor, and the expander 634 is also preferred tobe a turbine driving an electric power generator. Such generator must besynchronized to the frequency and phase of voltage in the electric powerline and to match that voltage value, very similar to other generatorsused in electric power grid. Other types of compressors and expandersbeside turbine type can be used as well.

FIG. 22 shows isothermal machines, one to increase pressure and one todecrease it. In the machine to increase pressure, a compressor 636driven by electric motor is used, and the resulting gas mixturereceiving power from the electric power line is both compressed andcooled. The heat is removed by a cooler 638. The amount of heat removedis equal, theoretically, to the electric energy delivered from theelectric power line. For large changes in pressure, severalserially-connected isothermal pressure changers can be used. In thiscase, they are called interleaved compressors. They are interleaved withcoolers.

The opposite process is used for reducing pressure isothermally. In thiscase, the gas mixture is expanded and this reduces both, its pressureand temperature. Change in temperature is compensated by heating. Again,the amount of heat delivered to the mixture is equal, theoretically, tothe amount of energy delivered to an electric power line by the electricgenerator driven by an expander 640. It is preferred to use turbines asboth, compressors and expanders, but other types can be used as well.

The system uses coolers 638 and heaters 642 in the isothermal machines.These are, in essence, heat exchangers. For isothermal operation, it ispreferred to use phase conversion of a working fluid to deliver orremove heat to and from gases passing through these heat exchangers.

This enables the system to process heat with near zero change intemperature.

Returning to FIG. 7, several examples of energy distribution lines usedin the present invention are shown. A first is an electric power linethat delivers power to all uses—the electrolyser and all electricmotors—and receives power from all sources—the electric power plant andall internal electric power generators.

Other lines are heat distribution lines. They deliver heat or acceptheat from various sources and uses of heat. Each line preferablyincludes two parts, a liquid part and a vapor part. When heat must bedelivered from a line, then vapors are taken into a heat exchangerdedicated to accept this heat, condense in this heat exchanger andrelease heat, and condensed liquid is delivered in the other half of aheat distribution line. When heat must be accepted, the reverse processis used, liquid is evaporated into vapors.

In the present process, examples of temperatures at which phaseconversions occur are:

a) At a temperature of the RWGS reactors—heat distribution line RWGS(RWGS-line);

b) At a temperature of the FT reactors—heat distribution line FT(FT-line);

c) At a temperature of water in the electrolyser—heat distribution lineE (E-line);

d) At ambient temperature—heat distribution line A (A-line); and

e) At a temperature of carbon dioxide separation—heat distribution lineC(C-line).

The following are examples of working fluids for these lines:

a) Ethylene glycol for RWGS-line;

b) Water for FT-line, or a substitute at higher temperature, likeethylene glycol;

c) Water for E-line;

d) Ammonia for A-line; and

e) Ethylene for C-line.

FIG. 23 shows a combination of a condenser and evaporator, machines 616and 624 on FIG. 20. The condenser part is a heat exchanger 652 throughwhich a gas mixture is passed. Heat from the gas mixture is removed byevaporation of a working fluid via an evaporator 654, and this causescondensation of a desired component of a mixture, pre-conditioned forsuch condensation, in a collector part 656 of the heat exchanger 652.Liquefied gas is collected and expunged into an evaporator, where thereverse process takes place. Heat is delivered to the evaporating heatexchanger from the same heat distribution line. Theoretically, thisprocess of condensation and evaporation of the separated gas is energyneutral.

FIG. 24 shows how electric energy is distributed and recycled. Line 1 isthree-phase electric distribution line. It is fed by the main source ofelectric power per FIG. 6, preferable powered by a fast breeder typenuclear reactor. It is also powered from residual energy released in theFT reactors by the generator 716 on FIG. 27. Electrolyser cells per FIG.14 are major users of the electric power. All expander-generator devicesused in adiabatic temperature changes and isothermal pressure changesare feeding this line, and all compressor motors used in adiabatictemperature changes and isothermal pressure changes are fed from thisline. Naturally, all other accessory motors and generators are attachedto this line. We show some areas of processing where various motors andgenerators are used.

FIG. 25 shows how heat distribution and recycling lines are used. In theRWGS-line, heat is delivered by a heat pump 710 shown on FIG. 27, heatbeing derived from energy released in the FT reactors. This heat is usedto heat the RWGS reactors as depicted on FIG. 10. All heaters andcoolers shown on FIG. 22 that are used in isothermal pressure changes ofincoming and outflowing gases in these reactors use or deliver heat fromor to this line.

In the FT-line, heat is delivered via the heat exchanger 714 on FIG. 27,heat being derived from energy released in the FT reactors. All heatersand coolers shown on FIG. 22 that are used in isothermal pressurechanges of incoming and outflowing gases in these reactors use ordeliver heat from or to this line.

In the Electrolyser-line, heat is delivered via the heat exchanger 712on FIG. 27, heat being derived from energy released in the FT reactors.Main user of heat is heater/boiler for electrolyser water on FIG. 28.All heaters and coolers shown on FIG. 22, that are used in isothermalpressure changes of incoming and outflowing gases in the electrolyser,use or deliver heat from or to this line.

FIG. 26 shows two more heat distribution and recycling lines. One is aline operating at ambient temperature. All heaters and coolers shown onFIG. 22, that are used in isothermal pressure changes of incoming andoutflowing gases at ambient temperature, use or deliver heat from or tothis line. All evaporators and condensers shown on FIG. 23 of a gasseparator like steam are either getting heat from this line or deliverheat to this line. There is also a receiving end of a heat pump bringingexcess heat from the carbon dioxide separation line. All unused heat inthe overall plant will be delivered to this line and dissipatedprimarily as waste heat.

The other line on FIG. 26 is the carbon dioxide separation line. Allheaters and coolers shown on FIG. 22, that are used in isothermalpressure changes of incoming and outflowing gases at a temperature closeto carbon dioxide separation by liquefaction, use or deliver heat fromor to this line. All evaporators and condensers shown on FIG. 23 forcarbon dioxide separation are either getting heat from this line ordeliver heat to this line. The carbon dioxide separation line is usednot only for separation of carbon dioxide from effluent gas on theoutput of the RWGS reactor, but also for separation of C₃ and C₄hydrocarbons and residual carbon dioxide in the effluent gas of the FTreactor. There is also an excess heat collecting end of a heat pumptaking excess heat from the carbon dioxide separation line into theambient line.

Preferred Gas Separation and Processing

Carbon dioxide can be delivered to this apparatus typically by apipeline at a typical gas pipeline pressure of 50 bar and at ambienttemperature. For input into the RWGS subassembly, carbon dioxide shallbe heated to the RWGS temperature, 400° C. in this embodiment, andoperating pressure like 25 bar. To accomplish this, all or some of theprocesses 610 through 614 on FIG. 20 can be used.

Hydrogen from the electrolyser is coming out at 130-150° C. temperatureand 20-30 bar pressure, and must be conditioned for inputting it intothe RWGS subassembly. To accomplish this, all or some of the processes610 through 614 on FIG. 20 can be used.

On the output of each RWGS reactor, steam must be separated. This mustbe done at low temperature in order to remove most of the steam. In thisembodiment, this is ambient temperature. To accomplish this separation,all or some of the processes 610 through 614 and the process 616 on FIG.20 can be used. Also, processes 614 and 616 can be combined in onemachine. After separation, gases must be reconditioned for furtherprocessing using all or some of the processes 618 through 622 of FIG.20.

Carbon dioxide present in the effluent stream on the output of the thirdsteam separator in the RWGS subassembly can be separated using a varietyof processes such as amine absorption, carbonate absorption, pressureswing absorption, adsorption, gas permeation, additive-assistedcryogenics (e.g., Ryan-Holmes), or three phase cryogenics (CFZ). Whenliquefaction is used to separate majority of carbon dioxide, then all orsome of the processes in FIG. 20 can be used. In this embodiment,temperature T₁ is ambient, temperature of condensation T₃ is in −55° C.range, temperature T₄ is equal to the FT reactor temperature, 220° C. inthis embodiment, and temperature T₆ is equal to the RWGS reactortemperature, 400° C. in this embodiment.

Hydrogen to the FT reactor subassembly is coming from the electrolyserat 130-150° C. temperature and 20-30 bar pressure, and must beconditioned for 220° C. and 20 bar as preferred in this embodiment. Toaccomplish this, all or some of the processes 610 through 614 on FIG. 20can be used.

If carbon monoxide is supplied to the FT subassembly, it is likely to bedelivered via a pipeline at a typical pressure of 50 bar and at ambienttemperature. For input into the FT subassembly, carbon monoxide shall beheated to the FT temperature, 220° C. in this embodiment, and expandedto operating pressure like 20 bar. To accomplish this, all or some ofthe processes 610 through 614 on FIG. 20 can be used.

On the output of each FT reactor steam is separated at ambienttemperature in this embodiment. To accomplish this separation, all orsome of the processes 610 through 614 and the process 616 on FIG. 20 canbe used. Also, processes 614 and 616 can be combined in one machine.After separation before the second FT reactor, gases must bereconditioned for further processing using all or some of the processes618 through 622 of FIG. 20.

After the second FT reactor, steam along with heavier residualhydrocarbons is also separated at ambient temperature. To accomplishthis separation, all or some of the processes 610 through 614 and theprocess 616 on FIG. 20 can be used. Also, processes 614 and 616 can becombined in one machine.

Following this separation, C₃ and C₄ hydrocarbon gases must be separatedusing all or some of the processes 610 though 616 on FIG. 20. At lowcontent of carbon dioxide and syngas, condensation can be at ambienttemperature. Otherwise, it must be at lower temperature rather thanhigher pressure. In a preferred embodiment, there is C-line forcondensation of carbon dioxide and it is used for condensation of C₃,C₄, and CO₂ in this mixture. Consequently, by changing pressure of aseparated liquid, CO₂ will evaporate first and be processed throughprocess 624 through 630 of FIG. 20 to be input into the RWGS assembly.The condensate of C₃ and C₄ compounds can be used in liquid form or, ifdesired, evaporated and conditioned to gas using all or some of theprocesses 624 through 630 on FIG. 20. Finally, the residual of C₁ and C₂hydrocarbons, syngas, and other gases must be conditioned for input intoa controllable release 322, again using all or some of the processes 618through 622.

Then, in the recycling loop of the FT subassembly, the gases must beconverted from an input condition of ambient temperature and pressure inthe controllable release to the input conditions of the first FT reactor−220° C. and 20 bar in this embodiment. Again, all or some of theprocesses 610 through 614 on FIG. 20 can be used.

Finally, if oxygen from the electrolyser is to be delivered for usesoutside of this plant, then it also must be conditioned. It is comingout from the electrolyser at a temperature of 130-150° C. and pressureof 20-30 bar. For delivery by a pipeline, oxygen must be conditioned toa typical pipeline pressure of 50 bar and ambient temperature. Toaccomplish this, any or all processes 610 through 614 on FIG. 20 can beused.

Similarly, for oxygen delivery to the burner-generator, steam separationthere, and delivery of carbon dioxide back to the input, the processesdescribed herein for such purposes and presented on FIG. 20 can be used.

Similarly, hydrogen for use in refining can be processed in the same wayas described, but for different output temperature and pressure.

Recycling of Heat from the Fischer-Tropsch Subassembly

Exothermic heat of the reaction in Fischer-Tropsch reactors is the majorsource of energy to drive all gas processing in this plant and source ofadditional electric energy for water electrolysis. On FIG. 27, we show acooling loop for the FT reactors. In this embodiment, vapors of theworking fluid to cool the reactors are distributed for condensation inseveral heat machines.

The first machine 710 is a heat pump pumping heat derived fromcondensation of vapors to the RWGS heat distribution line. On the outputof the condenser, working fluid is in a liquid phase at condensationtemperature.

The second machine is a heat exchanger to heat water to the electrolysertemperature. Again, this heat is delivered by condensation of a workingfluid. This process can use all or some of the processes 610 through 616on FIG. 20, and the electric power that is generated is deliveredthrough an electric power distribution line to the electrolyser. Theoutflowing liquid is reheated from the FT-line and compressed to matchthe FT reactors temperature and pressure.

The third machine is delivering heat into an FT heat distribution lineby condensation if such heat is required to balance heat flow in thisline.

The residual vapors are driving an electric power generator 716 withoutlet temperature at preferably an ambient level. The electric energyis delivered to the electric power line and via this line to theelectrolyser to add to the energy delivered by the electric power plant.Liquefied working fluid is recompressed and reheated to the pressure andtemperature of this liquid coming out from other condensers, andreturned back to the FT reactors for cooling them by evaporation. Wateris reheated using heat from FT heat distribution line. The example ofthe working fluid is water. At higher FT operating temperatures, otherfluids like ethylene glycol can be used.

Water Feed to the Electrolyser

On FIG. 28, we show processing of water to feed the electrolyser. Wateris coming from multiple sources. It is preferred to recycle as muchwater from the other processes in this plant, specifically from the RWGSreactors steam separators, from the FT reactors steam separators, fromthe burner-generator steam separator, and any water collected inrefining. All these streams of water and incoming water are at differenttemperatures, most of them around ambient temperature, but theelectrolyser water is at 130-150° C. and compressed to 20-30 bar.Additionally, at above certain high current density the electrolysermust be cooled, and at below certain current density the electrolysermust be heated.

In the preferred embodiment, we use water heating/boiling andcompression to condition this water to such temperature and at theelectrolyser pressure that this water either absorbs electrolyser excessheat or delivers the excess heat. When in the mode of heat delivery,part of it can be even vaporized to deliver more heat to electrolyserwater via condensation. When in the mode of heat absorption, watertemperature is lower than in the electrolyser. For vapor compression,all or some of the processes 610 through 614 on FIG. 20 can be used. Forwater heating, E-line heat is used.

Main Controls

Electronic control is inherent to the system of the present invention100. Controls include a physical layer and control computers withsoftware incorporating control algorithms. The physical layer comprisessensors and actuators. Each functional block of the present invention100 has sensors pertinent to its function—like gas flow, or specific gasor liquid flow, pressure, temperature, velocity, among others.

The actuators are pumps for condensers and evaporators, electricgenerators driven by expansion turbines, electric motors drivingcompressors, gas and liquid flow throttles or valves, mechanicalregulators like variable vanes in turbines, and others as required forperformance of a certain function.

It is preferred to use distributed computer processing with redundancyto assure safety and timeliness of control.

A list of main control functions of this invention 100 include:

-   -   Control complete conversion of incoming carbon dioxide into        carbon monoxide in the RWGS assembly;    -   Control gas discharge on the output of the Fischer-Tropsch        assembly to maintain a predetermined level of hydrocarbon or        other gases in this output stream;    -   Control of hydrogen supply to the input of the RWGS assembly;    -   Control of hydrogen supply to the input of the FT assembly;

FIGS. 29-32 illustrate various systems of the control processes 1500 ofthe present invention 100. FIG. 29 illustrates control of the RWGSassembly. The essential purpose of control of the RWGS assembly is tosubstantially as possible convert incoming carbon dioxide into carbonmonoxide using feedback control.

Flow of incoming carbon dioxide is controlled via a throttling device1502 having a regulating element driven by the power driver 1504. A flowmeter 1506 is provided for incoming carbon dioxide after throttle 1502.A second flow meter 1508 is provided for carbon monoxide on the outputof the RWGS assembly. Outputs of both meters are fed to inputs of anerror amplifier 1512 as shown, and those inputs are calibrated in molarvelocity. The output of this amplifier drives power driver 1504.

If amount of carbon monoxide becomes smaller than carbon dioxide, theerror amplifier output reduces drive of the throttle and less carbondioxide flows making difference between both flows smaller, with errorbandwidth of this negative feedback loop.

In FIG. 30 is shown the control of the FT assembly. The essentialpurpose of the control of the FT assembly is to maintain certain levelsof hydrocarbon or other gases like syngas on the output of the assembly,with the ultimate purpose of minimizing discharge of syngas out of theFT assembly recycling loop.

A control gas flow meter 1522 on the output of the FT subassembly islocated prior to the splitter 322. Signal from this flow meter is fedinto an error amplifier 1526, where it compares with a reference level.Output of this amplifier feeds a power driver 1528 that controls flowcontrol element 1532 of the splitter 322.

This is a negative feedback loop, and in a steady state condition, theflow control device 1532 allows enough effluent gas to escape such thatthe amount of control gas is kept steady as defined by the referencelevel. If there is more control gas, then the flow control device opensmore and reduces this excess, and vice versa.

In FIG. 31 is shown the control of hydrogen supply to the RWGSsubassembly. The essential purpose of this control is to supply enoughhydrogen for the desired H₂/CO ratio on the output of the RWGSsubassembly.

Flow of incoming carbon dioxide is measured by the same flow meter 1506.There is another flow meter 1544 of hydrogen. Output of carbon dioxideflow meter is fed into a multiplier 1546 that multiplies signal by thedesired ratio of hydrogen versus carbon dioxide on the input of the RWGSsubassembly. In a preferred embodiment it is between 1.5 and 3.2.Signals from the multiplier and from the hydrogen flow meter are fed toan error amplifier 1548, and those inputs are calibrated in molarvelocity. Output of this amplifier feeds the driver 1552 to control ahydrogen flow regulator 1554, which can be as simple as a throttle.

Hydrogen is supplied from the electrolyser. It is a negative feedbackloop. Its static condition is to allow flow of hydrogen when the outputfrom amplifier 1548 is zero. If the amount of carbon dioxide supplydecreases, then there will be a signal on the output of the amplifier1548 to reduce flow via 1554. The reverse is true as well.

FIG. 32 shows the control of hydrogen supply on the input of the FTsubassembly. The essential purpose of this control is to regulate theratio of hydrogen to carbon monoxide between the separator 328 and thesplitter 332 for the desired production of hydrocarbons in the FTsubassembly.

Carbon monoxide flow is measured by a flow meter 1562 and hydrogen flowis measured by a meter 1564. Both meters are calibrated in molarvelocity. A signal from meter 1562 is fed to a multiplier 1566 where themultiplier coefficient represents the desired ratio of hydrogen tocarbon monoxide on the output. In a preferred embodiment, it isapproximately two, similar to the ratio on the input of the FTsubassembly, and varies as a function of operating conditions of aspecific type of the FT reactor hereby described.

Outputs of the multiplier 1566 and the flow meter 1564 are fed to anerror amplifier 1568. Output of this amplifier feeds a control driver1572 that powers a regulating mechanism of a hydrogen flow controldevice 1574 that can be as simple as a throttle. Hydrogen is fed fromthe electrolyser through this flow controller 1574 to the input of theFT subassembly.

This is a negative feedback loop. With zero output of the amplifier1568, the amount of hydrogen delivered to the FT subassembly is justright for the desired coefficient of the multiplier. If more hydrogen isdetected on the output of the FT subassembly, then flow control device1574 will be regulated to pass less hydrogen, and vice versa.

There is also a water level controller in the tub. It regulates a waterdrain mechanism installed in the drain. It is a conventional controllerused to maintain liquid level in storage tanks by drainage.

Electric Energy Usage

A summary table, TABLE 1, illustrates the calculation of efficiency andelectric energy usage as described herein.

TABLE 1 Summary Table of Energy Flow in kJ Carbon oxide feed CO₂ CO₂ COCO Efficiency boundary Min Max Min Max Energy for electrolysis 853 753578 510 Energy for RWGS reaction  41  37 — — Energy from FT reaction(146) (176) (146) (176) Energy for processing 200 150 133 100 TOTALELECTRIC 948 764 565 434 ENERGY (TEE) High heating value (HHV) of 670680 670 680 hydrocarbon compounds Energy efficiency, %  71  89 119 157(HHV/TEE) Electric energy use per unit of    1.4    1.1    0.84    0.64high heating value (TEE HHV) Excess (Deficit) of TEE, %  40  10  (16) (36)

In Table 1, the calculations are shown for two species of carbon oxides.For each species, all values as explained in the following exemplarydescription and leading to minimum efficiency are combined in onecolumn, and all values leading to maximum efficiency in another.Efficiency is defined as a ratio of the high heating value of combustionof hydrocarbon compounds (HHV) to the total electric energy supplied tothe process and the plant from an external source (TEE). Electric energyuse is defined as a reciprocal value of efficiency, as TEE over HHV.

In the last line of Table 1, an excess or deficit of electric energy isshown. For example, in a case of using carbon dioxide as an input andhaving minimum efficiency, 40% more electric energy will be requiredthan the high heating value of combustion of hydrocarbon compoundsproduced. In a case of using carbon dioxide as an input and havingmaximum efficiency, only 10% more electric energy required.

In case of carbon monoxide as an input, it is evident that substantiallyless electric energy will be required, as carbon monoxide has certaincombustion energy (versus carbon dioxide having none). For this reason,in case of carbon monoxide as an input and having minimum efficiency,16% less electric energy will be required than the high heating value ofcombustion of hydrocarbon compounds produced. In a case of using carbonmonoxide as an input and having maximum efficiency, 36% less.

The following is a description of the entries of Table 1, wherein forsimplicity, all energies are shown per one carbon dioxide mole convertedinto hydrocarbon compounds.

Electric energy required for electrolysis of water is between 274 and286 kJ per mole of hydrogen, as a function of temperature and undercurrent density providing isothermal operation.

In the preferred embodiment, it is estimated that this will be 275 kJ.3.1 moles of hydrogen are required to recycle one mole of carbondioxide, thus, 853 kJ of electricity will be required, which is forisothermal operation. For lower current densities, this amount ofelectric energy will be lower, for an example of up to 100 kJ lower. Insuch a case, this deficiency will be supplied from the other processesin this plant. Naturally, for higher current densities, there will be aneed for more electric energy and additional heat must be removed. Someof this heat can be recycled into feeding an electrolyser electricallyvia electric power generation. Naturally, all heat can't be recoveredand total energy consumption will increase.

The RWGS reaction is moderately endothermic and requires 37-41 kJ permole of converted carbon dioxide, as a function of operating conditions.This is another process that can use heat produced in this plant.

The Fischer-Tropsch reaction is highly exothermic and produces 146-176kJ per carbon monoxide mole converted. This reaction is a major sourceof heat in this plant, methods and systems.

Other energy needs comes from energy dissipated in the processes thatare difficult to recover like losses in bearings, electric motors,transformers, rectifiers, radiation and convection losses, and the like,and from the difference in enthalpy of incoming and outflowing products.It is important to note that it is only losses in reversible processingof gases and liquids that count due to processing per FIG. 20. For thisreason, it is estimated that these losses are in the range of 150-200 kJper mole of carbon dioxide.

Output from the FT reactors is a mixture of hydrocarbon compounds withdifferent combustion energies. For this estimate, the high heating valueof combustion is used as water is used for recycling. In a mixture ofcompounds, this energy is on the order of approximately 670-680 kJ perone converted carbon dioxide mole.

Using all these values, the amount of input electric energy iscalculated per amount of high heating value of combustion of hydrocarboncompounds produced using that electric energy in the process and systemhereby described. This range is between 1.4 and 1.1 when only carbondioxide is used on the input. In turn, this means that the system needsbetween 10 to 40% more electric energy from an external source than iscontained in high heating value of combustion energy of hydrocarboncompounds with end products carbon dioxide and water.

This energy usage is favorably comparable with the energy usage of coalto liquid conversion—in the range of 2.5- and gas-to-liquid (GTL) energyusage in the range of 1.7. In both cases, the input is high heatingvalue of either coal or gas.

In the present system, there is a much lower usage of electric energywhen carbon monoxide is used from an external source, versus usingcarbon dioxide. In this case, the system will need one mole less ofhydrogen, and no heat for the reverse water gas shift reactors. Thenenergy required for water electrolysis will be in the range of 275kJ/mol, times 2.1 moles, for 578 kJ. In addition, the amount of lossesin gas processing will be reduced at least by one-third due toelimination of the RWGS process and carbon dioxide separation process,so it will be 100 to 130 kJ. This results in that external electricenergy needs are between 0.64 and 0.84 of high heating value ofhydrocarbon compounds.

To achieve such beneficially low usage of externally suppliedelectricity, the following major internal energy flows are implemented:

-   -   From Fischer-Tropsch to RWGS, using heat pump;    -   From Fischer-Tropsch to the electrolyser, as condensation heat        of steam, if required;    -   From Fischer-Tropsch to all process heat uses;    -   From Fischer-Tropsch to the electrolyser, using residual heat        for electric power generation;    -   From internal gas expanders-generators to internal        compressor-motors; and    -   From internal gas/liquid coolers to internal gas/liquid heaters        using phase conversion of working fluids

Systems-Wide Preferred Alternatives

In addition to using the FT reactor(s) to convert syngas into liquidfuels, it can be desirable to produce major components of natural gas,methane. This can be accomplished using a catalysed reaction

CO+3H₂→CH₄+H₂O  (7)

In addition, other various hydrocarbon substances can be produced fromsuch syngas, as commonly known in the art.

In another preferred embodiment of the present invention, a plant can belocated in proximity to natural gas fields, to take carbon dioxide, anddeliver CH₄. In many gas wells, there is substantial amount of carbondioxide, perhaps and some of them are closed for that reason. The RWGSand FT processes disclosed can in some instance be bypassed, using aSabatier reaction:

CO₂+4H₂→CH₄+2H₂O  (8)

In this process, similar amounts of heat are released as in the FTprocess (per carbon oxide mole) and conversion takes place atapproximately 300° C.

Two different reactions can be used replacing the disclosed FT and RWGSprocesses. The first is the Lurgi process, also known as the Carnolprocess, can be used. The second is the methanol-to-gasoline (MTG)process.

While in the reverse water gas shift reaction, carbon dioxide is reactedwith hydrogen to produce carbon monoxide and water, the Lurgi or Carnolprocess uses the same reactants as the reverse water gas shift reactionwith different catalysts and reaction conditions to produce methanol.Thus, in another embodiment of the present invention, the RWGS reactioncan be substituted for the Lurgi or Carnol process, being:

CO+3H₂→CH₃OH+H₂O  (9)

The methanol produced from this reaction is then used in the MTG processwith high selectivity for light hydrocarbons forming basis of gasoline.

While the invention has been disclosed in its preferred forms, it willbe apparent to those skilled in the art that many modifications,additions, and deletions can be made therein without departing from thespirit and scope of the invention and its equivalents as set forth inthe following claims.

1-80. (canceled)
 81. A system for producing hydrocarbon compoundscomprising at least the following units: a) a reverse water gas shiftreactor assembly supplied with hydrogen gas and carbon dioxide gas togenerate a syngas, that is a mixture of at least carbon monoxide gas andhydrogen gas, water steam, and residual carbon dioxide gas; b) a unitfor generating a mixture of at least hydrocarbon compounds from at leastcarbon monoxide gas and hydrogen gas; characterized in that the reversewater gas shift reactor assembly comprises: a) a first reverse water gasshift reactor supplied with hydrogen gas and carbon dioxide gas, whereinthe molar ratio of hydrogen to carbon dioxide is more than one, togenerate a first syngas stream comprising a mixture of at least carbonmonoxide gas and hydrogen gas, water steam, and residual carbon dioxidegas; b) a unit for condensing at least some water steam from the firstsyngas stream to generate a second syngas stream; c) a second reversewater gas shift reactor supplied with the second syngas stream togenerate a third syngas stream; d) a unit for condensing at least somewater steam from the third syngas stream to generate a fourth syngasstream, which is supplied to the unit for generating a mixture of atleast hydrocarbon compounds.
 82. The system of claim 81, wherein theoperating temperatures of the reverse water gas shift reactors isbetween 350° C. and 500° C.
 83. The system of claim 81, wherein thereverse water gas shift reactor assembly comprises more than twosequentially arranged reverse water gas shift reactors with units forcondensing at least some water steam from the exiting syngas streamtherebetween.
 84. The system of claim 83, wherein the operatingtemperatures of the reverse water gas shift reactors is between 350° C.and 500° C.
 85. The system of claim 81, further comprising one or moreseparating units, which may be provided after a reverse water gas shiftreactor, and before a following reverse water gas shift reactor or aunit for generating a mixture of at least hydrocarbon compounds, toseparate at least some carbon dioxide from the stream of syngas exitingfrom at least one of the reverse water gas shift reactors and enteringinto a following reverse water gas shift reactor or unit for generatinga mixture of at least hydrocarbon compounds.
 86. The system of claim 83,further comprising one or more separating units, which may be providedafter a reverse water gas shift reactor, and before a following reversewater gas shift reactor or a unit for generating a mixture of at leasthydrocarbon compounds, to separate at least some carbon dioxide from thestream of syngas exiting from at least one of the reverse water gasshift reactors and entering into a following reverse water gas shiftreactor or unit for generating a mixture of at least hydrocarboncompounds.
 87. The system of claim 85, further comprising a unit forsupplying removed carbon dioxide gas to at least one of the precedingreverse water gas shift reactors.
 88. The system of claim 86, furthercomprising a unit for supplying removed carbon dioxide gas to at leastone of the preceding reverse water gas shift reactors.
 89. The system ofclaim 87, wherein at least a portion of the removed carbon dioxide issupplied to the first reverse water gas shift reactor.
 90. The system ofclaim 88, wherein at least a portion of the removed carbon dioxide issupplied to the first reverse water gas shift reactor.
 91. The system ofclaim 81, further comprising a separating unit to separate carbondioxide from a stream exiting the unit for generating a mixture of atleast hydrocarbon compounds, wherein the stream comprises a mixture ofat least hydrocarbon compounds and carbon dioxide, and wherein theseparated carbon dioxide is supplied to the first reverse water gasshift reactor.
 92. The system of claim 83, further comprising aseparating unit to separate carbon dioxide from a stream exiting theunit for generating a mixture of at least hydrocarbon compounds, whereinthe stream comprises a mixture of at least hydrocarbon compounds andcarbon dioxide, and wherein the separated carbon dioxide is supplied tothe first reverse water gas shift reactor.
 93. The system of claim 85,further comprising a separating unit to separate carbon dioxide from astream exiting the unit for generating a mixture of at least hydrocarboncompounds, wherein the stream comprises a mixture of at leasthydrocarbon compounds and carbon dioxide, and wherein the separatedcarbon dioxide is supplied to the first reverse water gas shift reactor.94. The system of claim 86, further comprising a separating unit toseparate carbon dioxide from a stream exiting the unit for generating amixture of at least hydrocarbon compounds, wherein the stream comprisesa mixture of at least hydrocarbon compounds and carbon dioxide, andwherein the separated carbon dioxide is supplied to the first reversewater gas shift reactor.
 95. The system of claim 81, further comprising:a) a unit for generating carbon monoxide made by an optional reactionprocess that converts carbon dioxide to carbon monoxide; and b) a unitfor providing a portion of the stream exiting a reverse water gas shiftreactor to a unit for generating a mixture of hydrocarbon compounds fromat least carbon monoxide gas and hydrogen gas.
 96. The system of claim83, further comprising: a) a unit for generating carbon monoxide made byan optional reaction process that converts carbon dioxide to carbonmonoxide; and b) a unit for providing a portion of the stream exiting areverse water gas shift reactor to a unit for generating a mixture ofhydrocarbon compounds from at least carbon monoxide gas and hydrogengas.
 97. The system of claim 85, further comprising: a) a unit forgenerating carbon monoxide made by an optional reaction process thatconverts carbon dioxide to carbon monoxide; and b) a unit for providinga portion of the stream exiting a reverse water gas shift reactor to aunit for generating a mixture of hydrocarbon compounds from at leastcarbon monoxide gas and hydrogen gas.
 98. The system of claim 86,further comprising: a) a unit for generating carbon monoxide made by anoptional reaction process that converts carbon dioxide to carbonmonoxide; and b) a unit for providing a portion of the stream exiting areverse water gas shift reactor to a unit for generating a mixture ofhydrocarbon compounds from at least carbon monoxide gas and hydrogengas.